This technique is used for many other health problems when a food trigger is suspected. To track down whether any foods contribute to cluster headaches, you can avoid the common migraine triggers and then, if necessary, use an elimination diet, as described in the previous chapter. In fact, doctors used to diagnose cluster headaches by injecting a small amount of histamine under the skin and waiting for the headache to start about a half hour later. Lithium prevents attacks in about 40 percent of patients. But you can be aware of times when you are vulnerable to headaches and take preventive action, which for some people may mean medications. If cluster headaches tend to arrive just when you are relaxing, that does not mean that you will need to stay at work twenty-four hours a day, never take a vacation, and lie awake for fear of a sleep-induced headache.